Batch inclusion packages are widely used to contain materials such as carbon black, titanium dioxide powder, elastomers (rubbers), polystyrene pellets and other chemicals. The batch inclusion packages minimize dust health hazards and possible fire hazards, as well as waste, since the entire package and its contents are processed during use of the contents. The batch inclusion package has numerous requirements when used in such a manner. These include compatibility with the material to be contained, low melting temperature, a narrow softening range, and extrudability.
U.S. Pat. No. 4,248,348 (Butler et al.) discloses a package comprising an article (such as an unvulcanized rubber) packaged in a film. The film is made from an ethylene/vinyl acetate copolymer containing an antiblock agent. U.S. patent '348 teaches that polyethylene film is not suitable for overwrapping bales of rubber, because when the bale (including the film wrapper) is charged into a suitable mixer, the polyethylene film is not sufficiently dispersed and causes defects in the end product.
Similarly, U.S. Pat. No. 5,120,787 (Drasner) discloses a method of compounding a rubber by using a bag or liner made from an ethylene/vinyl acetate copolymer. The bag or liner is directly compounded into the mixer and becomes part of the rubber compound.
U.S. Pat. No. 4,394,473 (Winter et al.) discloses packages comprising an article (e.g., unvulcanized or vulcanized rubber) packaged in a bag made from syndiotactic 1,2-polybutadiene containing an antiblock additive. U.S. patent '473 also teaches that the use of polyethylene bags results in incompatibility problems.
EPA 0 270 902 (The Dow Chemical Company) discloses the use of bags made from copolymers of at least one olefin monomer (e.g., ethylene) and acrylic or methacrylic acid, or ionomers thereof, used to package particulate elastomer materials.
Branched, high pressure low density polyethylene (LDPE) and blends of LDPE with small amounts of traditional (i.e., Ziegler polymerized) linear low density polyethylene (LLDPE), typically less than 10 percent LLDPE, are sometimes used to make batch inclusion bags which are used to contain carbon black. The carbon black is then used to make tires. However, the melting and softening characteristics of LDPE limits its use as a batch inclusion packaging material.
Use of traditional LLDPE in batch inclusion is also severely limited because of its relatively high melting point and broad softening range.
We have now discovered that a new class of polyethylene overcomes the difficulties associated with use of traditional LDPE and LLDPE in batch inclusion packaging materials.